//
// Created by wze-zero on 2024/9/12 012.
//
#include <iostream>
#include <iomanip>

using namespace std;

int main() {
    int n, m = 0;
    double sum = 0;
    cin >> n;
    for (int i = 1; i < n + 1; ++i) {
        i % 2 == 0 ? m -= 2 * i - 1 : m += 2 * i - 1;
        sum += (double) 1 / m;
    }
    cout << fixed << setprecision(3) << sum << endl;
    return 0;
}